Shift Work Sleep Disorder

Shift Work Sleep Disorder (SWSD) is a circadian rhythm sleep disorder that commonly affects people who work non-traditional hours that involve overnight, early morning, or rotating shifts.

Our careers in aviation, the emergency services, medicine, engineering and security, to name a few professions can demand we work through the nocturnal hours. Human beings, however, are not designed to function optimally during the night. The human body is designed to be at its optimal performance in energy, alertness, concentration and other aspects of mental and physical capability during the day, aligned with our circadian rhythm. [1]

International research identifies the ‘Inability to sleep’ as one of the most common health complaints globally, often second only to cold/cough or respiratory issues. [2]

How Misalignment Becomes a Disorder

Circadian misalignment occurs when our body's internal clock is out of sync with the natural light-dark cycle, which can affect sleep quality. For example, when people try to sleep during the day due to work schedules, exposure to daylight can disturb their natural sleep-wake rhythms. 

Shift Work Sleep Disorder

SWSD, as defined by the International Classification of Sleep Disorders, Third Edition (ICSD-3), is a circadian rhythm sleep-wake disorder. It is characterized by insomnia or excessive sleepiness, or both, which are directly linked to a work schedule that overlaps with the typical time for sleep. [4]

Excessive sleepiness, or Hypersomnia, refers to feeling unusually tired or drowsy during waking hours, even after what should be a sufficient amount of rest. Circadian misalignment with daylight exposure during daytime sleep often leads to chronic insomnia (characterised by difficulty falling or staying asleep at least three nights per week for three months or longer) and excessive sleepiness. This is considered a disorder when symptoms of chronic insomnia and excessive sleepiness last over three months and disrupt daily life, such as causing difficulty concentrating at work, impairing social interactions, or increasing the risk of accidents. [2-3]

SWSD affects our circadian rhythms, which are physical, mental, and behavioural rhythms that follow a 24-hour cycle. Interruption in our circadian rhythm leads to disruption in the timing of sleep. When this occurs, there is difficulty adjusting to different sleep/wake schedules. One common problem is that insomnia symptoms (persistent difficulty falling asleep, staying asleep, or waking too early despite having enough time for sleep) in SWSD can arise from circadian misalignment. Other symptoms  include:

Shift Work Sleep Disorder (SWSD) and insomnia disorder are closely related but remain distinct conditions, which makes diagnosis challenging. Both involve sleep disturbances, but SWSD is specifically tied to a person's work schedule disrupting their circadian rhythm—symptoms typically appear when the individual works nights or rotating shifts. In contrast, insomnia disorder is characterised by ongoing difficulty in falling or staying asleep, or poor sleep quality, that persists regardless of changes in routine or external factors.

To help differentiate: 

• SWSD: Sleep problems are directly linked to the shift schedule. For example, a doctor working night shifts may have trouble falling asleep during the day, but once on regular daytime hours or during holidays, their sleep returns to normal. 

• Insomnia disorder: Sleep difficulties persist even when the person is not working shifts or is on holiday. For instance, someone may struggle to sleep whether they are working, on annual leave, or during weekends, indicating an ongoing issue not solely caused by their work schedule. Because symptoms of SWSD can sometimes evolve into chronic insomnia—where sleep problems continue even on days off—it can be difficult to distinguish between the two, especially when both disorders coexist or overlap. [5]

Cognitive Behavioural Therapy for Insomnia

Cognitive Behavioural Therapy for Insomnia (CBT-I) is widely recognised as the "gold standard" first-line treatment for chronic insomnia, as recommended by leading medical bodies such as the American College of Physicians . This structured, non-pharmacological therapy works by targeting and changing problematic behaviours and thoughts related to sleep. Notably, CBT-I has demonstrated a 70–80% success rate in improving sleep, according to clinical studies published by the American College of Physicians, which lends strong credibility to its effectiveness. [6]

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References

[1] KM-Human Factors Engineering. 2015. Shift work and our internal biological clock. https://km-humanfactors.com/nl/the-science/shift-work-and-our-biological-clock/

[2] Folia Medica. May 2025. Chronic insomnia – beyond the symptom of insufficient sleep. https://foliamedica.bg/article/151493/

[3] Cleveland Clinic. April 2023. Shift Work Sleep Disorder (SWSD). https://my.clevelandclinic.org/health/diseases/12146-shift-work-sleep-disorder

[4] The National Library of Medicine. 2016. Shift Work and Shift Work Sleep Disorder. https://pmc.ncbi.nlm.nih.gov/articles/PMC6859247/

[5] Cognitive-Behavioural Therapy for Insomnia (CBT-I) Across the Life Span. 2022. CBT-I Protocols for Shift Workers and Health Operators. WILEY Blackwell. 

[6] Guy’s and St Thomas’ Specialist Care. 2026. Cognitive behavioural therapy for insomnia (CBTi). https://guysandstthomasspecialistcare.co.uk/treatments/cbti-for-insomnia/